Without limiting the scope of the invention, its background is described in connection with pedicle screws.
In rigid severe spine deformity with coronal or sagittal decompensation, translation of the spinal column is necessary for restoration of trunk balance as well as deformity correction. However, the conventional correction methods, such as posterior correction only or anterior release and posterior instrumentation, are usually unsatisfactory. Therefore, a more aggressive approach, such as reconstructive techniques, is necessary. In 1922, Maclennan1 first illustrated vertebrectomy and demonstrated an apical resection from a posterior-only approach with postoperative casting for the treatment of severe scoliosis. Several authors2-8 have subsequently reported their experience with vertebrectomy, mostly for congenital scoliosis. In 1987, Bradford9 performed both anterior and posterior vertebral column resection (VCR) with spinal shortening and posterior instrumentation and fusion demonstrating excellent restoration of coronal with relatively few complications. Leatherman6 introduced a two-stage anterior and posterior correction procedure for congenital spinal deformity. Bradford and Bochie-Adjei10 also reported a single stage anterior and posterior resection of hemivertebra and spinal arthordesis. However, the anterior-posterior vertebral column resection (VCR) has disadvantages such as long operative time, potential significant blood loss, and risk of intraoperative neurologic impairment due to the spinal column segment instability during the resection and the correction procedure.
In 2002, Suk11-13 introduced a technique of a single posterior approach to perform VCR (PVCR) that offered significant advantages over the combined anterior-posterior VCR. The surgery consisted of temporary stabilization of the vertebral column with segmental pedicle screw fixation, resection of the vertebral column at the apex of the deformity via the posterior route followed by gradual deformity correction and global fusion. In the surgical technique, multiple pedicle screws were utilized proximal and distal to the vertebral resection to securely fix the spine prior to any bony resection. Provisional single rod placement is performed during the bony resection to prevent sudden spinal column translations which may result in spinal cord injury. The vertebral column resection and deformity correction were carried out either by exchanging the temporary precontoured rods one by one or by in situ rod bending. However, these technique have a number of disadvantages: 1) the risk of intraoperative mishaps due to the instability resulting from exchanging the temporary rods may produce spinal cord injury; 2) limitation in deformity correction secondary to a “one-time” correction maneuver utilized using the Suk technique; 3) short segment fixation using the provisional rods since multiple exchanges prevent long rod utilization; and 4) additional surgical time necessary with multiple removal and insertion of the temporary provisional rods.
One such fixation system is taught in U.S. Pat. No. 7,220,262, issued to Hynes. Briefly, the spinal fixation system and related methods include pedicle screws secured in two columns, one along each side of the spine. Cross support rods have ends connected to pedicle screw heads. A longitudinally extending rod is supported on the cross supports and recessed in the cavity created by removal of portions of spinous processes, providing a reduced profile of the installed construct. Several types of cross supports are shown such as: arms from the screws inward to rings or yokes connecting the longitudinal rod; cross rods with ends connected to the screws and having centrally-located yokes for the longitudinal rod; cross rods with articulating longitudinal rod portions fixed or swiveled to them. These cross rods may have end portions angled posterior toward anterior to accommodate lateral positioned pedicle screws, but shorter cross rods without angled end portions enable medialized pedicle screw orientation.
U.S. Pat. No. 7,163,539, issued to Abdelgany, et al., is directed to a biased angle polyaxial pedicle screw assembly. Briefly, a pedicle screw assembly and method of assembly is taught that comprises a longitudinal member; a screw head comprising a bulbous end, wherein the screw head has a slot adapted to receive the longitudinal member; a bone fixator component comprising a concave socket having a biased angled top and a rounded bottom adapted to receive the screw head; a locking pin adapted to engage the screw head, the bone fixator component, and the longitudinal member; and a blocker adapted to engage the screw head and to secure the longitudinal member. Additionally, the bone fixator component may be configured as any of a bone screw and a hook.
Yet another system is taught in U.S. Pat. No. 6,488,681, issued to Martin, et al., for a pedicle screw assembly. Briefly, a stabilizing assembly is taught that includes a fastener having an upper end and a lower end, a head at the upper end, and at least one anchoring element extending between the upper and lower ends. The head includes a center, an underside including a first radial surface and a top side including a second radial surface. The first radial surface of the head defines a first radius from the center of the head and the second radial surface defines a second radius from the center of the head, the first radius being greater than the second radius. The assembly also includes a coupling element having an upper end and a lower end, the coupling element including a rod receiving opening extending from the upper end thereof being adapted to receive a stabilizing rod, a bore extending through the lower end of the coupling element for receiving the fastener, and a conical-shaped seat adjacent the lower end of the coupling element adapted to engage the first radial surface of the head when the fastener is positioned in the bore. A locking element associated with the coupling element is adapted to apply a force upon a stabilizing rod positioned in the rod receiving opening. As a force is applied to a stabilizing rod, the rod in turn, engages the second radial surface at the top side of the head for forcing the underside of the head against the conical-shaped seat of the coupling element so as to prevent further pivotal and rotational movement of the fastener and the coupling element relative to one another. In certain embodiments, the fastener may be a screw fastener having screw threads. In other embodiments, the fastener may include a hook.
United States Patent Application No. 20070270810, filed by Sanders is directed to a pedicle screw spinal rod connector arrangement. Briefly, a pedicle screw spinal rod connector arrangement is provided that includes in a body having an opening for mounting a head of an inserted pedicle screw. A bracket connected with the body forms a lateral restraint. A bridge is connected with and extends over the body. A spinal rod-receiving slot is provided between the bridge and the bracket. The connector arrangement also has a wedge axially offset from the pedicle screw moveable downward by a setscrew mounted with the bridge. The wedge imparts a locking force on the pedicle screw head and a generally lateral locking force on the spinal rod.
Yet another example is shown in United States Patent Application No. 20070233062, filed by Berry for a pedicle screw system with offset stabilizer rod. In this example, an improved pedicle screw system is provided with an offset stabilizer rod for the internal fixation of the spine. The pedicle screw system includes at least two multi-angle pedicle screw units adapted for anchored securement to patient bone, and an elongated stabilizer rod extending therebetween. Each pedicle screw unit includes a bone screw associated with an anchor bracket defining a laterally offset and upwardly open channel or trough for receiving and supporting the stabilizer rod. A securement member such as a set screw is fastened to the anchor bracket for compressively retaining the stabilizer rod within the bracket channel or trough. The securement member may also bear against the associated bone screw for compressively retaining the screw in position relative to the anchor bracket.